How to achieve desired results when using the subprocees Popen.send_signal(CTRL_C_EVENT) in Windows?

Question

In python 2.7 in windows according to the documentation you can send a CTRL_C_EVENT (Python 2.7 Subprocess Popen.send_signal documentation). However when I tried it I did not receive the expected keyboard interrupt in the subprocess.

This is the sample code for for the parent process:

# FILE : parentProcess.py
import subprocess
import time
import signal

CREATE_NEW_PROCESS_GROUP = 512
process = subprocess.Popen(['python', '-u', 'childProcess.py'],
                       stdin=subprocess.PIPE,
                       stdout=subprocess.PIPE,
                       stderr=subprocess.STDOUT,
                       universal_newlines=True,
                       creationflags=CREATE_NEW_PROCESS_GROUP)
print "pid = ", process.pid
index = 0
maxLoops = 15
while index < maxLoops:
    index += 1
    # Send one message every 0.5 seconds
    time.sleep(0.5)
    # Send data to the subprocess
    process.stdin.write('Bar\n')
    # Read data from the subprocess
    temp = process.stdout.readline()
    print temp,
    if (index == 10):
        # Send Keyboard Interrupt
        process.send_signal(signal.CTRL_C_EVENT)

This is the sample code for the child proceess:

# FILE : childProcess.py
import sys

while True:
    try:
        # Get data from main process
        temp = sys.stdin.readline()
        # Write data out
        print 'Foo ' + temp,
    except KeyboardInterrupt:
        print "KeyboardInterrupt"

If I run the file parentProcess.py I expect to get "Foo Bar" ten times then a "KeyboardInterrupt" followed by "Foo Bar" 4 times but I get "Foo Bar" 15 times instead.

Is there a way to get the CTRL_C_EVENT to behave as a keyboard interrupt just as SIGINT behaves in Linux?

After doing some reading I found some information that seems to contradic the python documentation regarding CTRL_C_EVENT, in particular it says that

CTRL_C_EVENT 0 Generates a CTRL+C signal. This signal cannot be generated for process groups

The following site provide more inforamtion about creation flags: Process Creation Flags.

Answer 1

This method of signal handling by subprocesses worked for me on both Linux and Windows 2008, both using Python 2.7.2, but it uses Ctrl-Break instead of Ctrl-C. See the note about process groups and Ctrl-C in http://msdn.microsoft.com/en-us/library/ms683155%28v=vs.85%29.aspx.

catcher.py:

import os
import signal
import sys
import time

def signal_handler(signal, frame):
  print 'catcher: signal %d received!' % signal
  raise Exception('catcher: i am done')

if hasattr(os.sys, 'winver'):
    signal.signal(signal.SIGBREAK, signal_handler)
else:
    signal.signal(signal.SIGTERM, signal_handler)

print 'catcher: started'
try:
    while(True):
        print 'catcher: sleeping...'
        time.sleep(1)
except Exception as ex:
    print ex
    sys.exit(0)

thrower.py:

import signal
import subprocess
import time
import os

args = [
    'python',
    'catcher.py',
    ]
print 'thrower: starting catcher'
if hasattr(os.sys, 'winver'):
    process = subprocess.Popen(args, creationflags=subprocess.CREATE_NEW_PROCESS_GROUP)
else:
    process = subprocess.Popen(args)

print 'thrower: waiting a couple of seconds for catcher to start...'
time.sleep(2)
print 'thrower: sending signal to catch'

if hasattr(os.sys, 'winver'):
    os.kill(process.pid, signal.CTRL_BREAK_EVENT)
else:
    process.send_signal(signal.SIGTERM)

print 'thrower: i am done'